This invention relates to surgical fastener for fastening body tissue, and more particularly to a fastener having improved tip structures for better penetration of the tissue to be fastened. This invention also relates to an improved tip which retains good penetration characteristics even after shrinkage due to annealing of the fastener. Additionally, an improved fastener with a trocar tip is disclosed.
Surgical fastening devices allow a surgeon to fasten body tissue by applying surgical fasteners. The fasteners, usually arrayed in rows, may be applied sequentially or simultaneously depending on the type of fastener applying instrument and the requirements of the surgical procedure. Surgical fasteners are often made of inert metals such as titanium and stainless steel. Metal fasteners are generally U-shaped staples, the legs of which are crimped for fastener closure when the staple is driven through the body tissue and into an anvil with staple crimping depressions.
Non-metallic fasteners are also known and may be preferable to metal fasteners in some procedures. Non-metallic fasteners may be made of polymeric material, and preferably bioabsorbable synthetic polymers. Bioabsorbable polymers offer a significant advantage in that they remain in the body tissue only as long as is necessary for tissue healing. After that the bioabsorbable fastener gradually degrades. A separate procedure for its removal is not required.
Polymeric materials generally do not possess the strength and ductility of metals. Hence, closure of the polymeric fasteners is achieved without crimping the fastener structure. Typically, polymeric fasteners are fabricated as two-part structures: a generally U-shaped fastener portion, and a corresponding retainer portion which engages and interlocks with the legs of the fastener portion. The legs or prongs of the fastener member are driven through one side of the tissue to be fastened and the retainer member interlocks with the prongs of the fastener member on the other side of the tissue to hold the entire fastener structure in place.
Surgical fasteners and fastener applying apparatus are disclosed in U.S. Pat. Nos. 4,060,089; 4,402,445; 4,534,352; 4,610,250; 4,667,674; 4,728,020; 4,932,960; Des. 280,931; Des. 280,932; Des. 286,180; Des. 286,441; and Des. 286,442, all of which are herein incorporated by reference.
A frequent goal in fastening tissue is achieving hemostasis along the fastener line. Hemostasis is achieved by exerting pressure on the tissue from both sides. If metal staples are used, that pressure (hereinafter referred to as "hemostatic pressure") is exerted by and between the base of the staple on one side of the tissue and the crimped legs on the other side of the tissue. In typical crimped metal staples no part of the staple extends beyond the ends of the base. Therefore, a second staple can be applied very close to the first staple, so that the bases of the two staples are in a line. In that case the gap between staples can be quite small so that hemostatic pressure is applied uniformly along the entire staple line.
In contrast, when two-part polymeric fasteners are used, hemostatic pressure is exerted by and between the retainer member and the backspan or crosspiece of the fastener member. In known two-part polymeric fasteners the prongs of the fastener member extend from the ends of the backspan. The retainer member is typically longer than the distance between the prongs and, therefore, must extend beyond the fastener member backspan. Accordingly, the backspans of adjacent fastener members lying in a line are separated by at least the sum of the distances by which adjacent retainer members extend beyond the associated fastener member backspans. Thus, there are gaps between adjacent fastener members. Full hemostatic pressure is not exerted on the tissue in these gaps.
One way to make up for the above-mentioned gaps in a line of polymeric fasteners is to provide fasteners with a crosspiece which extends beyond the span of the prongs so that the fasteners can be applied nearly touching each other such as disclosed, for example, in Korthoff et al., U.S. Pat. No. 4,667,674, issued May 26, 1987. Another way to make up for the above-mentioned gaps in a line of polymeric fasteners is to apply the fasteners in two parallel rows, with a linear offset between the rows so that the gaps in one row are opposite the bases of the fastener members of the other row.
U.S. Pat. No. 4,932,960 to Green et al. discloses a bioabsorbable two-part fastener having a fastener portion and a retainer. The fastener portion includes a locking surface oriented in the direction of the lengthwise extension of the fastener backspan, therein designated as an "X direction".
To facilitate the placement of multiple rows of fasteners it is desirable to have fasteners which are as narrow as possible. However, the narrower one makes a fastener of any given length and shape the weaker it is because there is simply less structural material. For this reason, the structural features of surgical fasteners which compensate for the lack of material by distributing or reducing stress become increasingly important as the fastener size is reduced.
In particular, stresses are created when the fastener portion is driven through body tissue. The fastener member prongs may tend to splay or spread apart as the prongs are forced through the tissue. Since the prongs must be precisely aligned and spaced apart in order to engage the corresponding apertures in the retainer portion, deformation of the prongs can cause failure of the faster and retainer portions to lock together, thereby resulting in bleeding from the loss of hemostasis and tissue holding.